As is exemplified in German Patent Application No. P 24 26 538, sewing machines having belt drives are known in the art. In this German Patent Application, the belt is driven by an intermittently rotating shaft which, in turn, is driven by an overrunning clutch mechanism. With such a drive, the feed rate is adjusted by changing the deflection or swing of the overrunning clutch. An inherent drawback with such mechanisms is the inconsist amount of overthrow. That is, at different sewing speeds there are different amounts of overthrow and, accordingly, different amounts of belt advancement resulting in a nonuniform workpiece feed.
German Patent Application No. P 28 48 123 illustrates another form of feed belt mechanism. This application discloses a continuously driven belt, the speed of which is variable. A series of gears and belts are employed for effecting this end. The gearing for changing the feed rate is complicated and thus, understandably, expensive to manufacture. Albeit the variable friction drive of the type disclosed is constant, this type of drive does not permit slippage between the work and the feed belt. Therefore, a gear system of the type disclosed is not applicable for intermittently moving a workpiece past a sewing instrumentality.
U.S. Pat. No. 3,435,790 to A. N. Hale is exemplary of a sewing machine device having an intermittent rotating drive shaft. Because of the form of locking connection disclosed in this device, there generally is no overthrow of the driving means. Such structure, however, permits only limited adjustability of the output.